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Abstract

A metallurgical process for producing a metallic implantable medical device, such as a stent, in a condition wherein the metallic alloy of the device has improved mechanical properties. The starting material is formed into an oversized tube which is drawn to finished outer diameter. The drawing process cold works the tube to produce a material having a high dislocation density and a yield strength that is above approximately 125 ksi. Next, the drawn tube is heat treated at a temperature of approximately one-half the absolute melting temperature of the alloy. The heat treatment causes dislocations to rearrange, forming sub-grains and re-crystallization of the grain structure. Upon cooling, a material is obtained having a yield strength between approximately 45-70 ksi and an elongation exceeding 40 percent. The material also has good resistance to fatigue fracture due to the fine grains and sub-grains that are established during the heat treatment.

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First Claim